My invention relates to lighting devices, to electric lamps, and to a lamp assembly comprising a light bulb and a bulb holder assembly for vehicular headlight and like applications. More specifically, my invention deals with such a lamp assembly featuring improved provisions for mounting a light bulb such as a halogen cycle incandescent lamp in place on a holder body of plastics material.
In an incandescent lamp assembly for vehicular headlight applications, it has been known to hold the light bulb by a molded plastic holder body of substantially tubular shape in order to be mounted to a reflector. The holder body is molded from a plastic by reasons of dimensional accurary obtainable and the close contact that can be realized between the holder body and the reflector by virtue of the pliancy of the plastic. Special consideration is needed in holding the light bulb of vitreous material by the plastic holder body. Conventionally, for this purpose, a metal made holder band has been wrapped around the pinch sealed base of the light bulb for resiliently engaging the bulb base by opposed pairs of bulb retainer lugs formed in one piece with the holder band. This holder band has been plasma welded to a metal made connector of tubular shape immovably engaged in the plastic holder body. It is thus seen that the light bulb has so far been supported by the plastic holder body via two metal made members, that is, the holder band and the connector.
A problem has heretofore been encountered in the choice of materials for the two metal made members through which the light bulb is coupled to the plastic holder body. The holder band, one of the two members in question, must resiliently engage the bulb base via the self biased retainer lugs formed integral therewith. High resiliency is therefore the first and foremost requirement of the material for the holder band. As far as resiliency is concerned, nickel silver is the most desirable material I know of the holder band. However, fabricated from nickel silver, the holder band cannot possibly be firmly joined to the connector by plasma welding even if the connector is of weldable material.
Austenitic stainless steels of certain specific compositions are better suited for plasma welding. When made from this type of material, the holder band would be positively welded to the connector but would lack in resiliency. The holder band would then be unable to securely hold the light bulb and, in the worst case, might crack or otherwise destroy the bulb base.